Almost 100 deaths occurred under the watch of an Italian nurse accused of murdering dozens of patients, health officials said.
The figure is several times higher than that of other nurses at the same hospital.
Police were initially investigating 38 suspect deaths at a hospital in Lugo di Romagna, near Ravenna, after an autopsy found poison in the system of an elderly woman in the care of Daniela Poggiali, a 42-year-old nurse from the nearby town of Faenza.
Detectives have now extended their probe to as many as 96 deaths that occurred during Poggiali's shifts in a 12 months period.
The developments came after health officials released patient mortality figures for each of the 39 nurses in service at the Umberto I hospital from April 2013 to April 2014.
Investigators in charge of the probe have described the results, which revealed Poggiali topped the list by a large margin, as "worrying", Ansa news agency reported.
Fifty patients died in her direct care in the period under consideration - almost three times more than those who passed under the watch of the nurse with the second highest patient mortally rate (17), according to Ravenna's Local Health Agency Unit (Ausl).
Another 46 patients died under the supervision of colleagues she was aiding or in beds she had otherwise access to during her shifts.
The finding prompted an investigation into the deaths of another 37 patients who passed away during the nurse's night shifts over the four months prior to that.
Police said that analysis revealed anomalies in at least 10 cases.
Prosecutors allege Poggiali took pleasure in killing patients who got on her nerves.
The nurse was fired earlier this year after sickening photos of her posing with thumbs up near an apparently deceased woman emerged.
The pictures, taken by a colleague who was also fired, were leaked to the press last week.
Poggiali is challenging the sacking, claiming the woman in the photos was alive. She also denies murder charges.